1. Technical Field
The present invention relates to a surface mount technology (SMT) techniques for fabricating printed circuit boards, and more specifically to a method and structure for temporarily attaching an electrical component to a pad located on a substrate of a printed circuit board, testing the component, removing and replacing the component if necessary, and making a final attachment of the component to the pad.
2. Related Art
Printed circuit boards are typically configured with many electronic components in close proximity with one another. While a given component may have passed a test for acceptability prior to its attachment to the circuit board, the component may not function properly after attachment due to attachment of a wrong component, a defective attachment, a misplaced attachment, a misorientation following attachment, or an erroneous interaction of the component with the overall electronic package. When an attached component is identified as not functioning properly, corrective action may require removal of such component. Thus, after all required components are mounted on a printed circuit board and the overall system is tested, the result of the testing may indicate that one or more components need to be removed and either replaced or reattached.
Prevailing methods in surface mount technology (xe2x80x9cSMTxe2x80x9d) for attaching and removing components utilize a heat source such as a soldering iron or hot air in conjunction with a solder paste that joins a component to a pad on a substrate of the circuit board. Such methods for removing components are time-consuming and costly, because the heat injected into the component-pad interface will, on occasion, cause damage to neighboring components as well as to the circuit board itself. In addition, the process of manually removing small components requires a fair amount of expertise. Thus, there is a need for a method that enables components on the substrate of a circuit board to be quickly and easily removed after in-line testing in a way that poses little risk of damage to the circuit board assembly.
The present invention provides a method of attachment and removal of components to and from pads located on the substrate of a printed circuit board, wherein the method enables components to be easily removed prior to final assembly without damaging the circuit board or components mounted thereon. The present invention temporarily joins components and pads by, for example, positioning a layer of electrically conductive adhesive (xe2x80x9cadhesive layerxe2x80x9d) between the component""s lead and the pad, wherein the adhesive is curable by exposure to radiation. Temporary attachment may be accomplished by directing a beam of radiation onto only a portion of the adhesive layer (xe2x80x9ctack areaxe2x80x9d) in order to cure only the tack area, wherein the tack area comprises a limited area of contact between the component""s lead and the adhesive layer. Since the tack area comprises a only a limited area of the adhesive layer""s surface area, the curing of the tack area creates a temporary attachment inasmuch as the user may subsequently remove the component, if necessary, by a small application of force without damaging the remaining area of uncured adhesive.
One method of directing radiation onto the tack area includes the use of a mask which causes the beam of radiation to cure only the tack area while leaving a remaining area of the adhesive layer uncured. The mask may comprise an opaque sheet with a hole, wherein the opaque sheet comprises material that is opaque to the beam of radiation, and wherein a portion of the beam passes through the hole onto the tack area.
Following temporary attachment of all required components to the substrate, the overall circuit board configuration may be tested. If the testing dictates that a component should be removed, the user may easily remove the component and either replace or reattach it. The final stage of the procedure cures the remaining area of adhesive by exposing the remaining area to radiation.
The present invention has the advantage of attaching a component lead to a pad by utilizing a radiation-curable, conductive adhesive layer between the component and the pad.
The present invention has the advantage of temporarily attaching a component to a pad by fastening only a portion of the component""s lead, rather than the whole lead, to the pad.
The present invention has the advantage of attaching a component to a pad by using radiation to cure the conductive adhesive layer that links the component to the pad.
The present invention has the advantage of utilizing a mask to cause radiation to strike a tack area of the adhesive layer while leaving the remaining area of adhesive uncured.
The present invention has the advantage of using a mask comprising an opaque sheet with a hole, wherein the opaque sheet comprises material that is opaque to the beam of radiation, and wherein a portion of the beam passes through the hole onto the tack area.